The present invention relates to adapting the functionality of nonwoven and other materials, suitable for use as components of an absorbent article, to enhance the liquid intake performance of such absorbent article. More specifically, this invention relates to determining optimal combinations of layer materials of an absorbent article for particular flow rate conditions to provide an improved absorbent article designed for specific flow conditions.
Absorbent articles, particularly feminine hygiene products such as sanitary napkins and liners, are designed to absorb and contain body exudates. Such disposable products generally are single-use items which are discarded after a relatively short period of usexe2x80x94usually a period of hoursxe2x80x94and are not intended to be washed and reused. Such articles usually are placed against or in proximity to the wearer""s body to absorb and contain various exudates discharged from the body. All of these products typically include a liquid permeable bodyside liner or cover, a liquid impermeable outer cover or backsheet, and an absorbent structure disposed between the bodyside liner and outer cover. The absorbent structure may include a number of different types of absorbent materials and layers, including a surge layer subjacent to and in liquid communicating contact with the bodyside liner, and an absorbent core typically formed of a blend or mixture of cellulosic pulp fluff fibers and absorbent gelling particles subjacent to and in liquid communicating contact with the surge layer. A transfer or distribution material layer may be provided between the surge layer and the absorbent core.
Desirably, personal care absorbent articles exhibit low leakage from the product and a dry feel for the wearer. Unfortunately, traditional feminine care products are not always adequate in preventing leakage for women that experience extremely heavy, heavy, and gush flow. It has been estimated that 60% or more of women with extremely heavy and heavy flow experience leakage with current feminine care sanitary pads. Leakage can result from a variety of performance deficiencies in the design of the product, or individual materials within the product. One cause of such leakage is an insufficient rate of liquid intake into the cover with subsequent transfer to the absorbent core, which functions to absorb and retain body exudates.
The liquid intake of a given absorbent product, and particularly the liner and surge materials forming the absorbent product, should thus be able to accept the expected liquid delivery rate into the absorbent product. The inability of the absorbent product to rapidly uptake liquid can result in excessive pooling of liquid on the body-facing surface of the bodyside liner before the liquid is taken up by the absorbent structure. Such pooled liquid can wet the wearer""s skin and can leak from around the sides or edges of the absorbent article, causing discomfort, potential skin health problems, as well as soiling of the outer clothing or bedding of the wearer.
One approach to improve overall liquid intake of absorbent articles has focused on the bodyside liner and its capacity to rapidly pass liquid to the subjacent absorbent structure. Nonwoven materials, including bonded carded webs and spunbond webs, have been widely used as bodyside liners. Such nonwoven materials generally are intended to be sufficiently open and/or porous to allow liquid to pass through rapidly, while also functioning to keep the wearer""s skin separate from the wetted absorbent underlying the liner. Attempts to improve the liquid intake of liner materials have included, for example, aperturing the liner material, treating the fibers forming the liner material with surfactants to enhance the wettability of the liner, and altering the durability of such surfactants.
Yet another approach has been to focus on various materials or layers placed between the bodyside liner and absorbent core material to enhance the core""s ability to rapidly intake fluid and to provide separation between the absorbent core and the bodyside liner adjacent the wearer""s skin. Such additional layer or layers, commonly referred to as a xe2x80x9csurgexe2x80x9d layer, can suitably be formed of thick, lofty nonwoven materials. Surge layers, particularly high loft, high bulk, compression resistant fibrous structures, provide a temporary retention or absorption function for liquid not yet absorbed into the absorbent core, which tends to reduce fluid flowback or re-wet from the absorbent core to the liner. A transfer or distribution material layer may be provided under the surge layer. This material is generally less hydrophilic than the other absorbent materials and is intended to spread liquid penetrating through the surge layer in the X-Y plane to more evenly distribute the fluid to the underlying absorbent core material.
Notwithstanding the foregoing, leakage in feminine care absorbent articles is still a problem, particularly for women experiencing heavy menstrual flows. The need exists for improvements in the liquid intake performance of the article materials, for example the liner materials and subjacent surge layer. In particular, there is a need for liner or cover materials that can provide improved handling of heavy liquid surges, particularly in feminine care products. The present invention relates to just such an improvement.
The present invention is directed to a protocol or test method for determining an optimal combination of materials for use in absorbent products, particularly feminine care products. The test method is particularly suited for improving the performance of feminine care products in heavy, extremely heavy, and gush menstrual flow conditions by optimizing materials selected for a particular menstrual flow condition.
The test method is based in part upon the realization that menstrual fluid is a complex, highly viscous, and non-homogeneous fluid and that traditional methods and parameters for measuring a material""s ability to absorb or pass fluid are not an accurate or reliable predictor of the material""s abilities with respect to menstrual fluid. The test method is also based on part upon the realization that accurate data can be obtained from in-vitro methods (i.e., lab or bench tests) under certain conditions and, thus, useful correlated data can be readily and quickly obtained. Traditional in-vivo tests are time consuming and may be misleading. For example, it is nearly impossible to predict or determine an actual menstrual flow rate of the women participating in the tests. There is no guarantee that a product intended to be tested for heavy menstrual flow conditions actually experienced such conditions, etc.
One embodiment of a test method according to the present invention for determining an optimal combination of materials for use in feminine care products under particular menstrual flow conditions includes an in-vitro method for determining an optimal combination of materials with respect to a particular menstrual flow condition for use in a feminine care absorbent article. The method includes selecting a subject flow rate corresponding to the average flow rate of menstrual fluid for a particular menstrual flow condition. A simulated menstrual fluid is provided to a flow rate controllable metering device, such as a syringe pump, and is dispensed onto a first combination of materials at the subject flow rate. The performance of the material combination is observed to determine if the particular combination adequately performs its intended purpose in the feminine care product at the subject flow rate. At least one of the materials in the combination is then changed and the steps of dispensing the simulated menstrual fluid and observing the performance of the combination of materials is again observed. Eventually, an optimal combination of the materials can be determined based on their performance when subjected to the simulated menstrual fluid at the subject flow rate.
The method may be used to determine the optimal material to be combined with a particular other material. For example, the test may be used to determine the optimal surge layer material to be used with a particular type of cover layer. In this instance, the cover material is held constant and the surge layer material is varied until the optimal surge material is determined.
Although the test method is particularly suited for determining an optimal combination of materials for use as a surge layer and cover layer for use in a feminine care product, it should be understood that the test is not limited to such a combination. For example, an optimal combination of absorbent core and surge layer materials may also be determined according to the inventive test method. Likewise, an optimal combination of cover layer and absorbent core materials may be determined.
Once the optimal combination of materials is selected for the subject flow rate, the flow rate may be changed to correspond to a different menstrual flow condition. It can then be determined how the combination of materials performs for different flow conditions. It may be that a combination of materials performs extremely well at a flow rate corresponding to a heavy menstrual flow, but performs poorly at light flow or extremely heavy flow conditions.
In an alternate embodiment, the test may be used to determine an optimal combination of materials only for a particular menstrual flow condition, for example an extremely heavy flow condition of about 20 ml/hr of menstrual flow, regardless of the combination""s performance at other flow rates. This method may be used in designing a particular flow specific product, such as an overnight heavy flow product.
In still an alternate embodiment, the subject flow rate may be selected as representative of a wide range of flow conditions.
Particularly for feminine care products, the method may include selecting the optimal combination of materials based on the combination""s ability to reduce leakage of the absorbent article, minimize wetness against a user""s skin, and increase menstrual fluid intake.
The method according to the invention will be described in greater detail below with reference to specific embodiments.